1. Field
Example embodiments relate to video data processing systems. Also, example embodiments relate to memory structures and/or accessing methods for video codec systems.
2. Description of Related Art
Compression coding and decoding technologies for motion picture signals are useful for sparing memory capacity in storing images, as well as enabling motion pictures to be transmitted through low-rate channels. Those compression coding and decoding technologies are now regarded as highly important in multimedia industries requiring several applications such as storage and transmission of motion pictures. In the meantime, to achieve compatibility of video information and extension of multimedia industry, the necessity of standardization for information compression has been rising until even now by accompanying with various applications on the industrial field of motion pictures.
There have been practical efforts for systemizing the global standards of motion pictures sprightly over the word, such that International Telecommunication Union-Telecommunication Standard Sector (ITU-T) established H.261 and H.263+ as the standards for serving motion pictures in the environment of wired/wireless communication, and International Standardization Organization (ISO) also provided motion picture standards such as MPEG-1, MPEG-2, and MPEG-4, where MPEG means ‘Motion Picture Experts Group’. With the rapid spread of radio communications since the developments of H.263+ and MPEG-4 standards, it was required to assure compression efficiency more enhanced than the conventional method and provide a technical specification for motion picture compression capable of accepting various communicating environments. Accordingly, ITU-T announced a ‘Request for Technical Proposal’ that is called H.26L specified in the next generation coding scheme, for which there were active studies by various-sized enterprises, institutes, and academic circles. Since that, the MPEG of ISO/IEC (International Electrotechnical Commission) entered the H.26L project in 2001. Thereby, ITU-T admitted the standard H.264 in May 2003 and then finally approved it as MPEG-4 Part 10 at ISO/IEC in August 2003.
The motion picture compression standard H.264 jointly established by ITU-T and ISO has been more advanced than the traditional standards such as MPEG-2 and MPEG-4 (Part 2) in flexibility to various network circumstances and efficiency of coding motion pictures. According to the estimation of engineers who participated in the standardization and implementation of motion pictures, it is regarded that the data compression rate by H.264 is 2˜3 times of MPEG-2 used in a current digital versatile disc (DVD) system, and higher than MPEG-4 by 1.5˜2 times. By the technology of H.264, it is possible to obtain image quality as same as DVD in a coding rate about 2 Mbps, or the same as home video cassette recorder (VCR) in a coding rate about 1 Mbps.
By applying the technology of H.264 to practical products and communication services, it greatly improves data transmission rate with reducing required image data capacity. While MPEG-2 is used in digital broadcastings and MPEG-4 is used in transmitting images of mobile phones, H.264 is expected to be used in applications needed to have higher compression rates above all.
In a general motion picture coding scheme, motion estimation and compensation is carried out in the unit of pixels of a predetermined volume size, i.e., a unit aggregation (M*N) composed by M horizontal pixels and N vertical pixels, instead of the unit of the whole image. Such a unit aggregation of pixels is called ‘macroblock’. In a general motion picture coding scheme, the macroblock is sized by 16 horizontal pixels and 16 vertical pixels (16*16).
Meanwhile, in the next generation motion picture compression technology, motion estimation and compensation is carried out in a smaller unit aggregation of pixels. A mode type of macroblock is determined in the range of sizes including 16*16, 16*8, 8*16, and 8*8. The 8*8 mode includes the sub-mode types of 8*4, 4*8, and 4*4. Therefore, if a block size of one macroblock is all in the 4*4 unit, it permits 16 motion vectors at maximum and needs to conduct motion estimation and compensation by block.
A typical way of encoding input motion picture data is to estimate pixel data of a current frame after storing pixel data of the previous frame in a memory. With higher resolution of motion pictures, it is trending toward the scheme that pixel data of the previous frame is stored in a memory out of a video codec and loaded into the video codec if there is a need to be used. Because of that, a memory bandwidth between the memory (i.e., an external memory) and the video codec is an important factor to performance of a motion picture processing system.